Detection of surfactants



Nov. 29, 1966 J. L DWYER 3,287,961

DETECTION OF SURFACTANTS Filed May 6, 1964 VACUUM PUMP INVENTOR. JAMES L. DWYER AT ORNEYS United States Patent 3,287,961 DETECTION OF SURFACTANTS James L. Dwyer, South Lincoln, Mass, assignor to Millipore Fiiter Corporation, Bedford, Mass., a corporation of Massachusetts Filed May 6, 1964, Ser. No. 365,246 3 Claims. (Cl. 7361.1)

This invention relates to the testing of water-immiscible liquids and in particular to the detection of surfactants in liquids such as internal combustion engine fuels.

Surfactants in fuels are generally deleterious because of their effect in causing water and other solid contaminants to become emulsified or suspended whereby impurities are more readily carried by the fuel. Where water has become emulsified, conditions favorable to the growth of microorganisms are also developed, which lead to a great number of difliculties.

The determination of surfactants is complicated by the great number of different chemicals of this type. Chemical tests alone are therefore not reliable, and measurements of behavioral characteristics of a fuel containing entrained water have given better results. Test procedures of this type have developed along two lines, the measurement of specific physical characteristics, such as fuel-water interfacial tension, and simulative tests. Tests of the first type require rather elaborate procedures but are principally hindered in failing to cover all of the factors encountered in actual field performance when surfactants are present.

In the simulative test procedures currently known an attempt is made to duplicate actual conditions encountered in the field and more reliable indication of surfactant effects are obtained. These procedures are not, however, adapted to simple and rapid on-site monitoring of the fuel.

The present invention provides a simplified simulative test which is based on the development of a novel type of separation system and on a procedure whereby that system can be used reliably to determine the presence of surfactants in the fuel and give an indication of. the effective amount present.

This invention is based on the discovery that an index to the presence of surfactants in a water immiscible liquid is given by the pressure and time relationship existing when water that has been separated from emulsion with the liquid is forced through a hydrophobic normally waon the hydrophobic filter surface and then forced through the filter while the time and pressure are measured. In the preferred embodiment a given quantity of distilled Water is first emulsified into the test liquid to assure that an amount of water sufficient for measurement is present. The water is then separated by drawingor forcing the mixture through a finely porous hydrophobic filter, which will collect and retain the water on the upstream side while permitting the test liquid to pass through. Con veniently the filter surface is held in an inverted or tipped position so that the water does not lie on and eventually cover the surface and interfere with the filtering action. When enough water to cover the filter surface has been separated on the upstream side of the filter, the apparatus is positioned with the filter forming the bottom surface covered by water, and the pressure difference is regulated to force the water through in a measured time interval.

The hydrophobic filter may be any of a number of finely porous hydrophobic materials known to the art, which may be selected on the basis of the known characteristic of materials of this type to retain water While permitting organic liquids to pass. A suitable filter will have pore size and hydrophobic characteristics not only effective to remove the water when the mixture is passed through at low pressure differential, but also that permits the water to pass through under a higher, yet measurable, pressure differential. In the preferred procedures the filtration pressure differential is created by a vacuum pump and limited to about 30 inches of Hg; therefore, a material through which pure water will flow at something less than 30 inches of Hg is required.

' The preferred hydrophobic filter material is a commercially available membrane filter, consisting typically of precipitated cellulose esters, having a void volume of about and a pore size of 0.80 microns. Treatment of the membrane filter with methyl chlorosilanes results in the formation of a polysiloxane surface coating which renders this material extremely water repellent. A membrane of this type will permit the passage of pure water when a pressure differential of about 24 inches of Hg has been reached.

A useful adjunct to the test procedure, which is also provided by this invention, facilitates the determination of the initial passage of water, by the appearance of contrasting color at the downstream side of the filter. For this purpose a porous backing member that has been i-mprcgnated with a water soluble, oil insoluble dye is provided to support the downstream side of the filter. The breakthrough of water results in the solution of some of the dye and the appearance of a cooled liquid at the filter outlet when the time and pressure conditions necessary for breakthrough have been reached.

A representative and preferred embodiment of this invention is described below. Reference is made to the accompanying drawings in which FIG. 1 is a schematic cross-section of a blender representative of the first step in the method of this invention;

FIG. 2 is a schematic cross-section in elevation illustrating the step of Withdrawing a sample of emulsified water and test liquid to collect a sample of emulsion Water;

FIG. 3 is a similar view illustrating the final test procedure in which the collected emulsion water is caused to breakthrough the filter under measured conditions of pressure and/ or time.

The apparatus for practicing this invention includes a high speed mixer 10 (see FIG. 1) and a filtration system (see FIGS. 2 and 3) comprising a filtration unit 12 and a variable vacuum source connected to the filtration unit 12 through a filtrate collection vessel 16.

The high speed mixer 10 may vbe a conventional blender in which a mixing jar 18 having an agitator blade 19 projecting through its bottom engages with a motor driven power unit 20. A cover 22 for the jar 18 should be provided.

The filtration unit 12 is typically formed of a bottom dish 24 having a drainage port 26 and a close fitting cover 28 having an inlet port 30, and contains a microporous filter film 32 arranged for filtration between the inlet and outlet ports. The filter film is conveniently supported on a porous support pad 34 which provides for drainageof filtrate from beneath the filter film.

The bottom dish 24 is preferably molded from a transparent plastic and is formed with an upright circular wall 36 terminating at its lower edge in an annular shoulder 38 which supports the margin of the filter film 32. The

6. cover 28 is similarly formed of a transparent plastic and includes a downwardly extending side wall 40 frictionally engaging the upright wall 36 and terminating in an edge abutting the margin of the filter film to hold it securely against the shoulder 38.

The porous support pad 34 is retained within the annular shoulder 38, with its top surface generally coplanar therewith, on a channelled bottom surface which provides for the flow of filtrate .to the outlet port 26.

In the preferred filter unit the support pad is a fibrous material such as blotting paper that has been impregnated with a water soluble dye such as methylene blue. This may be prepared simply by taking a standard grade of blotting paper, e.g. Hurlbut Grade 469, and dipping it into an aqueous solution containing'0.5 gram per liter of methylene bluev and then drying the paper. Discs cut of thist-o fit within the bottom area" of the filter unit provide for the development of a blue color once water has broken through the hydrophobic filter.

A convenient technique for producing hydrophobic filters consists in treating a commercially available cellulose ester membrane filter, suitably one having a pore size of, 0.80 micron, e.g. Millipore type AA, with a commercial organo halogenosilane as described by Patnode U.S. Patent No. 2,306,222. The resulting filter is thoroughly hydrophobic and well suited for use in the practice of this invention.

Filtration is effected by applying a vacuum to the filter unit 12 through a suction line 45, which connects to the outlet port 26 through a valve 46 and leads to the collection vessel 16. A variable vacuum within the vessel 16 is maintained by a vacuum pump 48 which connects through an adjustable vacuum regulator valve 50 to the vessel, by a line 52, into which is tapped a vacuum gauge 54.

In the preferred test procedure 500 cc. of the test liquid is placed in the thoroughly clean blender jar 18 and cc. of distilled water are added. With the cover 22 in place the blender is operated at high speed for about one minute, during which some, but generally not all, of the water becomes entrained or emulsified in the test liquid.

After the water and test liquid have been thoroughly agitated, a sample is drawn through the filter housing 12,

as illustrated in FIG. 2, by means of a tube 31 extending from the inlet port 30 into the water-test liquid mixture. In this operation the filter housing 12 is inverted so that the water separated from the mixture does not lie on the filter film 32.

In this operation the vacuum is adjusted to about 10.5 inches of Hg and the valve 46 in the outlet line from the filter unit is opened slowly so that the water-test liquid mixture is introduced gradually to prevent a vapor lock. When the filter unit is full of liquid the valve is opened entirely and all but about one-half inch of the liquid in the blender jar filtered through the filter. unit.

During the filtration process water emulsified in the test liquid is removed and collects in the top (lower portion) of the filter unit.

After the water has collected in an amount at least sufiicient to cover the filter film the filter unit is righted, preferably gradually with the vacuum applied so that the test liquid which will generally float-on top of the water, will be drawn off through the filter film before the wate covers it.

When the unit has been-righted a timer should be started, so that, if water will come through under the existing pressure (10.5 in. Hg) the measure of its time may be had. If Water does not appear in one-half minute the vacuum is increased by 2 inches (or any other convenient increasement) then again increased if water does not appear within one-half minute, and so on until the P ge of water is noted.

The pressure and time required for the passage of water provides a convenient index determinative of the presence of surfactants. Their presence is indicated when- I ever the breakthrough of water occurs at a lower pressure diiferential or in a shorter period of time than when ter collected from the water-test liquid mixture penetrates the filter more readily, i.e. in shorter time or under a lower pressure differential, the presence of a measurable quantity of surfactants is indicated. It has been found that as little as 0.05 part per million of some sur-i factants can be detected.

Although this invention has been described with spe-i cific reference to its preferred embodiment, it is conternplated that obvious modifications will occur to those skilled in the art and familiar with the principles of this.

disclosure and that such may be made without departing from the scope of this invention.

It is apparent for instance that water emulsified in the test liquid may be separated by techniques other than filtration such as by centrifuging and that the water collected from the test liquid could be forced through the hydrophobic filter by the application or generation of a positive pressure. water soluble colored substance in the support underlying the filter provides a convenient indication of the passage of water colorless substance e.g. ionizable salts, which can be detected chemically or electrically are also suitable for the same purpose.

Having thus disclosed my invent-ion and described its preferred embodiments in detail, I claim and desire to secure by Letters Patent:

1. The method of testing a water immiscible liquid for the presence of surfactants comprising adding water to said liquid and mixing it therewith, separating water from said liquid and placing it on a hydrophobic filter then applying a suflicient pressure differential across said filter to force the water therethrough, and measuring said pressure.

2. The method of testing water-immiscible liquids for the presence of dissolved surfactants comprising adding water to said liquid and agitating sufliciently to suspend the water therein, filtering the liquid and suspended .wa-.

ter through a waterrepellent filter to separate the water by collecting it at the upstream side of the filter in an filmand an outlet at the other side of said film connected.

by said outletto said. conduit, said housing being positionable to permit or prevent water in said housing to cover said film.

References Cited by the Examiner I UNITED STATES PATENTS 2,534,718 12/1950 Leaset a1, 73-38 2,844,025 7/1958 Joyce et a1. 7353 DAVID SCHONBE'RG, Primary Examiner.

In addition while the'presence of a Nesh 73--53 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,287,961 November 29, 1966 James L. Dwyer It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 10, for "permits" read permit line 35, for "cooled" read colored column 3, line 55, after "jar" insert is column 4, line 59, after "filter" insert housing Signed and sealed this 12th day of September 1967.

( AL) Attcst:

ERNEST W. SWIDER Attesting Offioer EDWARD J. BRENNER Commissioner of Patents 

1. THE METHOD OF TESTING A WATER IMMISCIBLE LIQUID FOR THE PRESENCE OF SURFACTANTS COMPRISING ADDING WATER TO SAID LIQUID AND MIXING IT THEREWITH, SEPARATING WATER FROM SAID LIQUID AND PLACING IT ON A HYDROPHOBIC FILTER THEN APPLYING A SUFFICIENT PRESSURE DIFFERENTIAL ACROSS SAID FILTER TO FORCE THE WATER THERETHROUGH, AND MEASURING SAID PRESSEURE. 